About HomeWaterCalc, and how to read it

What this site is

HomeWaterCalc publishes calculators, reference charts and buying guidance for home water treatment: water softeners, whole house filtration, sediment and carbon cartridges, reverse osmosis, well water treatment for iron, manganese, sulfur and low pH, ultraviolet disinfection, and the water testing that should come before any of it.

Everything here is compiled from published standards, regulatory limits, manufacturer specification sheets and the recurring themes in verified owner reviews. We do not test equipment in person and we never claim to. Any site claiming hands-on testing of forty softeners is telling you a story.

Three kinds of number, and why they are labeled separately

This subject mixes three kinds of figure that look identical on a page and are not equivalent. Every table on this site declares which one it is carrying.

• A published figure. The grains per gallon to milligrams per liter conversion of 17.1. The USGS hardness classification. Resin exchange capacity at a stated salt dose. The NSF/ANSI standard numbers and what each covers. EPA maximum contaminant levels and secondary standards. Federal maximum fixture flow rates. The NSF/ANSI 55 ultraviolet dose classes.
• A rule of thumb. Eighty gallons per person per day as a sizing figure. Regenerating about weekly. Adding three to five grains of compensated hardness per part per million of dissolved iron. Sizing a whole house filter by bathroom count. All taught everywhere and none of them published by any standards body.
• A figure from your own water test. Hardness, iron, manganese, pH, total dissolved solids, nitrate, bacteria. Nothing here supplies one and nothing here can override one.

What we refuse to publish

Where a published figure does not exist, we say so rather than estimating one. There is no EPA limit for hardness of any kind, because hardness is not a health contaminant. We publish no generic water volume per regeneration, because it is set by the control valve program and varies by more than a factor of two between units carrying the same nameplate. We publish no generic pressure drop, because every cartridge has its own published curve. And we never assert that a product removes a contaminant unless the manufacturer states a certification and a standard number.

What NSF certification actually means

A certification covers specific claims, not the whole unit. NSF/ANSI 42 is aesthetic effects such as chlorine taste and odor, and it is not a lead claim. 53 is health effects, certified claim by claim. 44 is softeners, and its efficiency rating only holds at the salt setting it was earned at. 55 is ultraviolet, where Class A delivers 40 mJ/cm2 for water not known to be safe and Class B delivers only 16 as a supplement to water already considered safe. 58 is reverse osmosis. 401 is emerging compounds. 372 is the lead content of a fitting rather than lead removal. The phrase "NSF certified" with no number attached is close to meaningless.

The safety line we do not cross

Nothing on this site diagnoses your water or says any product makes it safe to drink. That is a laboratory result rather than a property of a product. We describe what a contaminant is, what the published standard says, and what class of equipment is designed to address it.

Bacteria, nitrate, lead, arsenic and PFAS are not do it yourself topics. They are invisible and tasteless, so nothing tells you whether equipment has stopped working. Lead does not even have a maximum contaminant level: it has an action level of 0.015 mg/L, which is a trigger for utility action rather than a safe concentration, and the health goal is zero. For any of these, contact your local health department or a licensed water treatment professional before buying equipment.

How we make money

Through affiliate commissions on equipment people buy after reading. That never changes which product we recommend, and it is why several pages here tell readers not to buy something: plenty of households on moderate water do not need a softener, most do not need whole house reverse osmosis, and nobody needs ultraviolet on a well that has never tested positive. The affiliate disclosure sets this out in full.

Installation cost estimating is a separate question from equipment selection, and it lives on HouseProjectCalc rather than here.

Corrections

If a figure here is wrong, we want to know, particularly a published one. Contact us with the page and the source and it will be fixed.